fix recording reader was closed

reader_finished() is called when the reader closes, so the `readers -=
1` here was redundant and led to readers equalling -1 instead of 0.

lbrynet/blob/blob_file.py

@@ -168,7 +168,6 @@ class BlobFile(object):
         """
         if file_handle is not None:
             file_handle.close()
-            self.readers -= 1
 
     def reader_finished(self, reader):
         self.readers -= 1